Fuel flow proportioners



May 3, 1960 L. s. GREENLAND E1- AL l FUEL FLOW FROPORTIONERS Filed iviy6. 1958 2 Sheets-Sheet 1 s-llls] I I I I May .3, 1960 L. E. GREENLAND ETAL 2,935,078

FUEL FLOW PROPORTIONERS 2 Sheets-Sheet 2 Filed lvay 6, 1958 FUEL FLOWPROPORTIONERS Y Leonard Sidney Greenland, Tettenhall, William DonaldMcCourty, Wolverhampton, and Thomas Edwards, Codsall, England, assignorsto H. M. Hobson Limited, London, England, a British company ApplicationMay s, 195s, senat No. 733,301

Claims priority, application Great Britain May 7, 1957 18 Claims. (Cl.137-99) v and also upon the speed of rotation of the gears. When fuelflows through the gears there will be a pressure drop across them, and,due to this pressure drop and to a clearance between the tips and sidesof the gears and the charnber enclosing them, there will be leakagewhich will cause the proportioning to be inaccurate.

YIt is an object of the present invention to provide a fuel flowvproportioner of the above-mentioned type wherein the pressure dropacross each proportioning device and therefore the leakage and resultantmal-proportioning are substantially eliminated.

The invention accordingly provides a mechanicalfuel flow proportioner ofthe above type comprising in association with each source a owproportioning device matched to its source as regards both displacementand speed, said proportioning devices being operative to feed fuelcontinuously in predetermined proportions from the several sources to acommon outlet, a device responsive to the common output pressure of theproportioning devices from maintaining said output pressure at a prede-`termined value, and a device associated with each pro-` portioningdevice for maintaining its input pressure substantially equal to itsoutput pressure.

The proportioning devices may be independently driven but we prefer todrive them all at the same speed by a common prime mover as it is thennecessary only to match them in terms of displacement to theirrespective sources toobtain the required proportionality in the ow fromthe sources.

The invention includes a fuelflow proportioner of the above typeincluding in association with each source a ow proportioning devicecomprising inter-meshing rotors mounted to rotate within a casing andmatched as re'- gards displacement to the associated source, acompressed air motor connected to drive all the flow proportioningdevices, a control valve connected between the input to the air motorand a source of pressurised air, a device responsive to the commonoutput pressure of the ow proportioning devices for controlling saidvalve to maintainV said output pressure at a constant value, a pressureregulating valve disposed betweeneach ow proportioningl device and itsassociated source and a device sensitiveto the input pressure to each owproportioning device for course capable of changing speed in response tochange in the load on the ow proportioning devices.

Two alternative forms of fuel ow proportioners according to theinvention will now be described in detail by way of example withreference'to the accompanying drawings in which:

Fig. 1 is a block diagram of the first form of proportioner,

Fig. 2 is a diagrammatic view of said first form of proportioner butshowing one of the ow proportioning devices only,

Fig. 3 is a diagrammatic view similar to that of Fig. 2, showing thesecond form of proportioner and Fig. 4 is a detail view of the cammechanism utilised in both forms of proportioner.

Like reference numerals indicate like parts throughout the figures.

In Fig. 1 fuel supply tanks of differing sizes are indicated at 1, 2, 3and 4. lla, 1b, 1c and 1d are booster pumps for the tanks and the fuelfrom each of the tanks is supplied to an engine 9 through an individualintermeshing gear How proportioning device 10.

It is required 'that equal proportions of fuel shall ow from the tanks,so that, for example, when the system is used in an aircraft the massbalance of the aircraft Y shall not be disturbed. The exact proportionallowed to adjusting its pressure regulating valve to maintain said l owfrom each tank, as previously stated, is dependent upon the size andwidth of the gears of the associated proportioning device. The gears ofone of the proportioning device 10 are designated in Fig. 2 as 11 and12. The speed of the proportioning devices 10 in the illustratedembodiment is the same as they are all driven by a common motor 22 (Fig.2) driven by compressed air. As the tanks are of different sizes andthey will usually be in different head positions the booster pumps la-ldwill have toprovide different pressures. It therefore becomes necessaryto provide, in association with each proportioning device 10 a devicefor reducing these pressures to a common value in order to ensure thatall the proportioning devices will receive fuel at the same inputpressure, in view of the fact that the output pressures of all theproportioning devices 10 must necessarily be the same, having regards tothe fact that their outputs are supplied to a common manifold 8 (Fig. 2)leading to the engine 9 (Fig. 1). This pressure reducing device, shownat 13 in Fig. 2, comprises a diaphragm 14-having its lower face exposedto ambient atmospheric pressure applied thereto through inlets 7 and itsupper face exposed to the pressure existing at the downstream side of apressure regulating valve 15. The difference in pressure between ambientpressure and the required downstream pressure is balanced by a spring16, and the device 13 is so designed as to produce a pressure dropacross itself such that the -pressure downstream thereof is equal to theoutput pressure of the proportioning d'evice 10. A non-return valve 17,loaded by a spring 23, is provided at the inlet 6 to each proportioningdevice. At 18 there is shown a controlling device comprising a diaphragm19, having its upper face exposed througha duct 19A to thecommon outputpressure of the proportioning devices 10 and its lower face exposed toambient pressure applied thereto through an inlet 5, the differencebeing balanced by a spring 2G. The diaphragm 19j`is` operativelyconnected to a valve 21 for lcontrolling the ow of pressurised air tothe motor 22- through an orifice 121 communicating with a conduit 22Bleading from, for example, the compressor of a gas turbine engineinresponse to changes in the common outlet pressure ofthe` drives all ofthe proportioning devices through reduction gearing 23.

The operation of the proportioner is as follows:

Assume that the device 10 is proportioning correctly for any particularload due to the engine, for example a gas turbine engine. If, now, morefuel is called for in order to increase engine speed there will be aresulting drop in the output pressure of each proportioning device 10.This drop Vin pressure will cause the diaphragm 19 to move in an upwarddirection and allow more air from the compressor to be received by theair motor 22. The air motor 22 will, therefore, increase in speed andenable the proportioning devices 10 to provide the eXtra fuel requiredand raise their common output pressure to its previous value. As theoutput pressure rises the diaphragm 19 will return to substantially itsprevious position, but, of course, the compressor delivery pressure willnow be greater for the same opening of the valve 21,` so that the motor22 will maintain the increased speed. Obviously the diaphragm 19 andvalve 21 will move in the reverse direction in the event of increase inthe common -output pressure of the proportioning devices 1t)` to reducethe speed of the motor 22 until said output pressure has fallen to itspredetermined value.

Changes in altitude will alter the value of the input pressure to eachproportioning device 1t) supplied by its associated device 13. Eachproportioning device 10, is, however, controlled by its valve 15, whichis subject to a controlling air pressure which varies with altitude andzero pressure differential is accordingly maintained across theproportio-ning devices 1% at all altitudes.

' A by-pass valve 24 is provided between the input and the output ofeach proportioning device 1G and is normally held closed by a spring24A. In the event, however, of the device 10 seizing up, the valve 24can be manually opened so as to by-pass the seizeddevice 10 and allowYfuel to pass to the engine. In this case, of course, there will not beaccurate proportioning, but atleast the engine will receive an adequatesupply of fuel.

The non-return valve 17 associated with each proportioning device 10 isnormally held open by the booster pump pressure and will stay in theopen position so long as everything is working normally. The valves 17prevent seepage from one tank to the next in the case where the systemis at rest and a number of tanks of unequal head pressure are lled withfuel. In the event of booster pump failure, the non-return valve 17 willbe maintained open by engine suction and the associated gear pump 11, 12will then pump fuel to the engine with some decrease in accuracy ofproportioning, but this is preferable to no fuel at all. The valves 17,24 associated with each proportioning device are controlled by a camsystem 4t) illustrated in more detail in Fig. 4 land comprising a pairof cams 41, 42 which are actuable by an electrical actuator 25 of knowntype. This is capable of assuming alternative positions selected by asystem of push buttons for purposes of manual control and also bycontrols actuated by oats responsive to the level of fuel in the fueltanks, so as to adjust the position of the cams 40, 41 to effect thedesired control of the valves 17A and 24 and also, under certainconditions, to hold the pressure regulating valve fully open.

When the tanks are to be refuelled, fuel will be supplied tothe manifold8 which normally constitutes the common output manifold of theproportioning devices 10 Vand will, in consequence, rotate the gears 11and 12 thereof. These in turn will rotate the gears of the air motor 22and if it were not for the valve 21 pressure would be built up on whatis normally the input to the air motor until the air motor prevented thegears 11 and 1 2- rotating, which would, of course, stop the supply offuel to the tanks. When, however, fuel under the supply pressure reachesthe upper surface of the diaphragm 19 this will cause the valve 21 tomove downwardly and 4 thus vent the air motor to atmosphere by means ofa vent line 22A.

The cam 41 (Fig. 4) coacts with a rocker 49, pivoted at 43 and having anose 44 engaging a slot 45 in the upper end of the stem 26 of thenon-return valve 17. The cam 42 has a peripheral carn surface whichcoacts with a tappet 46 (Fig. 2) bearing on a pivotally mounted lever27. The cam 42 also has a face cam surface which coacts withY a rocker49 (not shown in Fig. 4 but indicated at 47 in Fig. 3) which bearsagainst the stem 4S of the by-pass valve 24.

During proportioning, the cams 41, 42 associated with eachproportiona'ry device occupy the position shown in Fig. 4 and thenon-return valve 17 is free to open under the pressure of the boosterpump, the by-pass valve 24 is maintained closed by its associated spring24A, and the lever 27 is maintained in a position such that the pressureregulating valve 15 assumes a position determined by the associateddiaphragm 14 and spring 16. When, however, the tanks are to be refuelledvia the proportioner, each of the actuators 25 is caused, by actuationof the appropriate push-button, to impart clockwise rotation to its cams41, 42 thereby causing the cam 41 to actuate the rocker 49 to lift theassociated non-return valve 17 to the open position. The clockwisemovement imparted to the cam 42 does not result in opening of theby-pass valve 24 but nevertheless causes the lever 27 to be rocked tohold the pressure-regulating valve 15 fully open.

When any of the tanks has been filled, a float therein actuates contactsto cause the associated actuator 25 to rotate anti-clockwise beyond theoriginal position shown in Fig. 4 to a third position in which the cam42 opens the bypass valve 24. In this third position the cam 41 allowsthe non-return valve 17 to close under the action of its spring 23 andthe cam 42 releases the lever 27 so that the pressure regulating valve15 is again under control of its diaphragm 14 and spring 16. It will beappreciated that as the result of movement of the cams through theiron'ginal position on their way to the third position, the valve 17 willclose before the by-pass valve 24 is opened. During this small intervalof time, the by-pass valve 24 can open against its spring 24A to preventthe gears 11, 12 (acting as a pump) from building up excessive pressurein the associated chamber.

When all the tanks have been lled and it is desired to recommenceproportioning, push buttons associated with each of the actuators 25 areoperated to cause the associated cams 40, 41 to return to the originalposition shown in Fig. 4. Each actuator is provided with a further pushbutton which can be operated to cause the cams to move to theabove-described third position in which the cam 42 opens the bypassvalve 24 to cater for seizure of the gear pump 11, 12 as already noted.

An air separator tank 28 (Fig. l) is provided so that, in the event ofthe proportioning device 10 sucking in air during refuelling, this airwill pass up through a duct 29 to the top of the tank 28. The resultingdrop in the level of the fuel in the tank 28 will cause a oat 30 to movedownwardly and in so doing open a valve 31. The air pressure will causea non-return valve 32 to open and allow the air to escape to atmosphere.The non-return valve 32 is necessary to enable the system to bede-fuelled by, for example, a fuel bowser. If it were not for thenon-return valve 32 the suction created by the bowser would cause thevalve 31 to pull 0E, with a resulting drop in suction pressure. Thenon-return valve 32 prevents this as it is then sucked onto its seat.

The proportioner shown in Fig. 3 is similar in principle to that alreadydescribed, although the gears 111, 1212 of each proportioning devicev 10are of somewhat different shape. Under some circumstances, the actuator25 may be unable, when it is desired to refuel, to lift the non-returnvalve 17 and the pressure regulating valve 15 against the fuel pressure(eg. 50 p.s.i.) supplied by Y the refuelling bowser. Provision for thismay be made by the incorporation of a non-return valve which will opento by-pass the pressure regulating valve 15 during refuelling. In thearrangement shown in Fig, however, the pressure regulating valve 15 isprovided with a second diaphragm 50 of smaller area than the diaphragm14 and to the undersurface of which the refuelling pressure of thebowser is applied through a duct 51. The pressure so exerted on thediaphragm 50 vcounteracts the refuelling pressure acting on the uppersurface of the diaphragm 14 and assists the valve 15 to rise. Duringproportioning, the pressure regulating valve 15 will be held openagainst the fuel pressure acting on the uppei surface of the diaphragm14 by atmospheric pressure and the pressure of the spring 16, and thelower diaphragm 50 will be held down against the seat 52V by.

atmospheric pressure acting on its upper surface.

A non-return valve 53, having a restricted orifice 54 therein and loadedby a spring 55, is provided in the duct 51, and the non-return valve 17is provided with a relief valve 56 loaded by a spring 57. As already explained, the non-return valve 17 and the pressure regulating valve 15close at the conclusion of the refuelling operation and the relief valve56 can then open,'when necessary and provided the valve 17 has closedbefore the valve 15, to relieve the system of excess pressure. Therestricted orifice 54 in the non-return valve 53 ensures that-when theactuator 25 operates at the conclusion of refuelling to allow the valves17 and 15 to close, sufficient pressure is applied to the undersurfaceof the diaphragm 50 to ensure that the valve 15 will close after thevalve 17. A restrictor (not shown) is provided in the-port 7 to minimisethe tiow of fuel through it in the event of either of the diaphragms 14,15 rupturing.

v Air under pressure is supplied to the control valve 21 of the airmotor 22 through an orifice 58 controlled by an overspeed valve 59 andthen through normally open orices 60 and I61, controlled 'by anegative-g valve constituted by a Weight 462. formed with a central hole63. During certain manoeuvres of the aircraft, the force o-f gravity isneutralised and the fuel rises to the tops of the tanks leaving thebottoms of the tanks, from which fuel is fed by the booster pumps, fullof air. This would cause the air motor 22` to race but for the -factthat under these conditions the valve 62 moves to close the orifices 60,'61 and shut off the air supply to the motor 22. Of cou-rse, a springmay be provided beneath the valve 62 to overcome friction and facilitateupward movement of the valve 62 when gravity is neutralised. The airmotor 22 .may also tend to race under such conditions, for example whenthe fuel tanks are empty and the devices pump air instead of fuel. Thisis prevented by the overspeed valve 59.

The valve 59 is attached to a diaphragm 64 which is normally subjectedto equal -air pressures on its two sides and a spring A65 normally holdsthe valve 59' in the open position shown. If, however, the air motor 22overspeeds, iiyweights `66 on the shaft 67 of the air motor operate toopen a va'lve l68 which is normally held closed by a spring 69.w l Airis vthen `'allowed to bleed at a rate controlled by a restrictor 70 fromthe space to the left hand side of the diaphragm 64 through a conduit71, the valve 68 and a vent 72, whereupon the diaphragm `64 will move tothe left to cause the valve 59 to reduce the supply of air to the airmotor 22.

It is sometimes desired in an aircraft to provide facilities forseparate withdrawal of fuel from tanks in the Wings and from tanks inthe fuselage. Thus, while it is usual during takeoff to draw fuel fromall the tanks, it is often the practice thereafter to use up the fuel inthe fuselage tanks before further fuel is withdrawn from the wing tanks.In this case separate sets of proportioning devices, each with anassociated air motor, will be provided for the wing and fuselage tanks.The supply of fuel from the fuselage tanks may then be switched olf bystopping the backing pumps associated with wing tanks. Under thesecircumstances the non-return valves 17 of the associated proportioningdevices will tend to remain open under the suction pressure of theengine'and the proportioning devices will tend to act as pumps and toprevent this the by-pass valves 24 are opened by operation oftheappropriate push buttons associated with the actuators 25. Theproportioning devices then tend to overspeed and the governor mechanismshown in Fig. 3 responds by cutting off the air supply to the ai-r motordriving the proportioning devices for the wing tanks. If no suchgovernor mechanism is provided the air supply to the air motor may beout otf manually. Alternatively, arrangements may be made wherebyshutting-off of any backing pump automatically causes the associatedactuator 25 to move to o-pen the non-return valve 24.

If means are provided whereby the output manifold of the wing tankproportioning devices is cutoff from the engine simultaneously withstoppage of the Vwing tanks backing pumps, the non-return valves 17 willclose. Any pressure built up between the proportioning devices and thepoint at which the output manifold is closed will then act on the device18 and cause it to cut off the supply of air to the air motor.

What we clairn as our invention and desire to secure by Letters Patentsis:

l. A mechanical fuel flow proportioner for delivering fuel from aplurality of supply sources to a common outlet and including inassociation with each source a tlow pr'oportioning device comprisinginterrneshing rotors mounted to rotate within a casing and matched asregards displacementto the associated source, a compressed airmotor-connected to drive all the ilow proportioning devices, a controlvalve connected -between the input to the air motor and a source ofpressurized air, a device responsive to the common output pressure ofthe flow proportioning devices for controlling said valve to maintainsaid output pressure at a constant value, a pressure regulating valvedisposed between each flow proportioning device and its associatedsource and a device sensitive to Vthe input pressure to each iiowproportioning devicefor adjusting its pressure regulating valve tomaintain said input pressure substantially equal to said common outputpressure.

2. A fuel flow proportioner accord-ing to claim l, wherein thepressure-sensitive device associated with the controlvalve is adiaphragm subject at one side to the common output pressure and at theother to the load of a spring and wherein 4the control valve controlst-he effective area of an orifice forV supplying pressurised air to theairmotor.`

3. A fuel ow proportioner according to claim 1, whereinthepressure-sensitive device associatedl with each pressureregulating'valve is a diaphragm exposed at one side to said inputpressure and at the other to ambient atmospheric pressure and thepressure of a spring.

4. A fuel ow proportioner according -to claim 1 comprising an overspeedgovernor associated with the air motor and means controlled thereby forreducing the flow of pressurised air to the air motor when the air motoroverspeeds.

5. A fuel ilow proportioner according to claim 4, wherein said governorcontrolled means comprises an overspeed valve for controlling the iiowof pressurised air to the control valve, a spring loaded diaphragmsubject on both sides to the pressurised air for controlling theposition of the overspeed valve and a valve controlled by the governorand arranged to open to bleed air from said diaphragm when the air motoroverspeeds, thereby causing the overspeed valve to move to reduce theflow of pressurised air to the air motor.

6. A fuel flow proportioner according to claim l, comprising anegative-lg,7 valve arranged, when the proportioner is installed in anaircraft dying under conditions such that 7 gravity is neutralised, tocut off the supply of pressurised air to the air motor.

7. A fuel ow proportioner according to claim 1, wherein each source is afuel tank and comprising in association with each proportioning device aspring-loaded non-return valve situated upstream of the pressureregulating valve and adapted to open under the pressure of fuel suppliedto the proportioning device by a backing pump from its associated tank,a normally closed bypass valve and a cam system operative to open thenonreturn valve to allow of refuelling of the tank by reverse iiow offuel through the proportioning device, and to cause the non-return valveto close and to open the by-pass valve after the tank has been filled.

8. A fuel ow proportioner according to claim. 7, wherein the cam systemis also effective to hold the pressure regulating valve fully openduring refuelling but to allow it to close when refuelling is completed.

9. A fuel dow proportioner according to claim 7 or claim 8, comprisingan electric actuator' for the cam systern which is controllable to moveto different positions under the control of push buttons and also ofcontrols actuated by a iloat in the tank.

10. A fuel ow proportioner according to claim 9, wherein the actuator isoperative by push button control to open the by-pass valve in the eventof seizure of the proportioning device.

11. A fuel iiow proportioner according to claim. 8, wherein thepressure-sensitive device associated with each pressure regulating valveis a diaphragm exposed at one side to the input pressure to its flowproportioning device and at the other to ambient pressure and thepressure of a spring, and wherein the pressure regulating valve isconnected to a second diaphragm subject, during refuelling, to therefuelling fuel pressure in the direction tending to open said valve.

12. A fuel flow proportioner according to claim 11, wherein therefuelling fuel pressure is applied to the second diaphragm through aduct containing a non-return valve containing a restricted surface.

13. A fuel flow proportioner according to claim 7, comprising inassociation with each proportioning device an air separator tank forcollecting air drawn in by said device during refuelling and afloat-actuated valve in said tank to allow air to escape from the tankthrough a non-return valve.

14. A mechanical fuel ow proportioner fordelivering to a common outletfuel supplied from a number of sources at different pressurescomprising, in association with each source, a rotary flow proportioningdevice matched as regards displacement to its source, a deviceassociated with said proportioning device for maintaining its inputpressure substantially equal to its output pressure, and a normallyclosed by-pass valve which can be manually opened in the event ofseizure of the proporn eg sources at different pressures comprising, inassociation with each source, a rotary flow propoitioning device matchedas regards displacement to its source and a device associated with said.proportioning device for maintaining its input pressure substantiallyequal toits output pressure, a compressed air motor coupled to anddriving all of said proportioning devices, a valve controlling admissionof air to said motor from a source of pressurized air and a deviceresponsive to the common output pressure of said proportioning devicesfor controlling said valve to maintain said output pressure at aconstant value. e

16. A fuel flow proportioner according to claim l5,

lwherein said motor comprises a pair of intermeshing gears adapted to berotated to drive said proportioning devices by compressed air suppliedto the motor by said vaive and said valve is movable to vent said gearsto atmosphere to permit said gearsV to be driven in reverse by thezproportioning devices during refueliing of said sources.

17. A mechanical fuel flow proportioner for delivering to a commonoutlet fuel supplied from a number of sources at different pressurescomprising, in association with cach source, a rotary flow proportioningdevice matched as regards Idisplacement to its source and a deviceassociated with said proportioning device for maintaining its inputpressure substantially equal to its output pressure, rotatable motormeans connected to drive said proportioning devices, means responsive tothe common output pressure of said proportioning devices for controllingthe speed of said motor means to maintain said output pressure at aconstant value, said motor means being rotatable in reverse by saidproporticning devices to permit of refuelling of said sources by fuelsupplied through said proportioning devices, and means for evacuatingairfrom the fuel supplied to said proportioning devices duringrefuelling.

18. A mechanical fuel flow proportioner for delivering to a commonoutlet fuel supplied from a number of sources at different pressurescomprising, in association with each source, a rotary ow proportiom'ngdevice matched as regards displacement to its source, a deviceassociated with said proportioning device for maintaining its inputpressure substantially equal to its output pressure, a spring loadednon-return valve situated upstream of said maintaining Idevice andadapted to open under the pressure of fuel supplied to the proportioningdevice from its source and a normally closed bypass valve for allowingfuel to by-pass the proportioning device, driving mechanism for drivingsaid proportioning devices so that they `feed fuel continuously and inpredetermined proportions from the several sources to the Vcommonoutlet, and means responsive to the fluid pressure in said common outletfor adjusting the speed of said driving mechanism so as to maintain saidoutlet uid pressure constant.

References Cited in the tile of this patent UNITED STATES PATENTS

